It is known that the density of gaseous methane can be enhanced in a storage vessel with the use of a carbonaceous adsorbent material having pores in a specified and limited range of diameters. In addition, activated carbons with a good microporous structure, but undesired microstructure, show lower working capacity. Therefore, there is always a compromise between the microporosity of the adsorbent where the enhancement effect takes place and the bulk density of the adsorbent, which determines the filling capacity of the storage system. Thus, the essential and principal feature of this invention is to provide post-carbonization treatment procedures which are applied to existing and preselected microporous carbons, which as a result of these treatments, then exhibit increased enhancement properties as storage media for methane and natural gas.
U.S. Pat. No. 5,071,820 (Quinn) entitled CARBONACEOUS MATERIAL WITH HIGH MICROPORE AND LOW MACROPORE VOLUME AND PROCESS FOR PRODUCING SAME discloses a two-step procedure for making activated carbon that involves heating the carbon to 150-200.degree. C. in oxygen for 45-75 minutes, after which the oxygen is purged with nitrogen, and then the carbon is heated to 750-900.degree. C. in nitrogen for 15-45minutes. The process can be repeated depending on the extent of microporosity desired.
U.S. Pat. No. 5,614,460 (Schwarz) entitled MICROPOROUS CARBONS FOR FUEL GAS STORAGE discloses a method for making activated carbon, known as CNDS synthetic activated carbon, by using crystalline salts of aromatic sulfonates as precursors.
U.S. Pat. No. 5,385,876 (Schwarz) entitled ACTIVATED CARBONS MOLECULARLY ENGINEERED discloses a method for making microporous carbon adsorbent material using an inorganic matrix and active carbon supported within the matrix.
U.S. Pat. No. 5,372,619 (Greinke) entitled METHOD FOR STORING METHANE USING A HALOGENATING AGENT TREATED ACTIVATED CARBON discloses a method for making a halogenated or sulfonated active carbon which has a high storage capacity for methane.
U.S. Pat. No. 4,499,208 (Fuderer) entitled ACTIVATED CARBON ADSORBENT WITH INCREASED HEAT CAPACITY AND THE PRODUCTION THEREOF discloses a method for increasing the heat capacity of activated carbon by adding dense alumina and heating at an elevated temperature
U.S. Pat. No. 4,960,450 (Schwarz) entitled SELECTION AND PREPARATION OF ACTIVATED CARBON FOR FUEL GAS STORAGE discloses a method for making an activated carbon for enhanced sorption of hydrogen by washing the carbon in water or acid and then oxidizing the washed carbon in a stream of oxygen and inert gas at an elevated temperature.
U.S. Pat. No. 4,716,736 (Schwarz) entitled METAL ASSISTED CARBON COLD STORAGE OF HYDROGEN discloses a method for storing hydrogen by using a transition metal dispersed in activated carbon.
U.S. Pat. No. 5,360,461 (Meinzer) entitled POLYMERIC STORAGE BED FOR HYDROGEN discloses a hydrogen storage device using polymeric material and a metal hydride.
U.S. Pat. No. 5,626,637 (Baker) entitled LOW PRESSURE METHANE STORAGE WITH HIGHLY MICROPOROUS CARBONS discloses a method for storing hydrocarbon fuels by making chemically and thermally treating an activated carbon using potassium hydroxide.
U.S. Pat. No. 5,653,951 (Rodriguez) entitled STORAGE OF HYDROGEN IN LAYERED NANOSTRUCTURES discloses a composition comprising a solid layered nanostructure, preferably carbon, for storage of hydrogen.
U.S. Pat. No. 4,857,243 (Von Blucher) entitled PROCESS OF MAKING MICROSPHERULES OF ACTIVATED CARBON discloses a method of making activated carbon microspherules by kneading activated carbon particles of a size below 100 .mu.m together with a dispersion of a water-insoluble synthetic resin, pressing the mixture through a screen with a mesh size related to the size of the desired product, powdering the pressed material, and granulating and drying the resulting microspherules.
U.S. Pat. No. 4,921,826 (Juntgen) entitled PROCESS FOR PRODUCING AN ACTIVE CARBON CATALYST discloses a process for producing an active carbon catalyst by ammonia treatment of active carbons at a temperature above 350.degree. C. in an inert-gas stream until no SO.sub.2 development occurs.
U.S. Pat. No. 4,371,454 (Hisatsugu) entitled PROCESS FOR PREPARING SPHERICAL CARBON MATERIAL AND SPHERICAL ACTIVATED CARBON discloses a process for preparing spherical activated carbon from an admixture of pitch, amorphous carbon, and a viscosity-controlling agent.
U.S. Pat. No. 4,205,055 (Maire) entitled DUAL PORE-STRUCTURE ARTIFICIAL CARBON AND GRAPHITE discloses a process for making the material and the material itself which is an artificial dual pore-structured carbon suitable for use as a catalyst substrate or an electrode material consisting essentially of a macroporous agglomeration of strongly bonded microporous grains of carbon.
U.S. Pat. No. 5,242,879 (Abe) entitled ACTIVE CARBON MATERIALS, PROCESS FOR THE PREPARATION THEREOF AND THE USE THEREOF discloses an activated carbon tailored for decomposition of hydrogen peroxide, hydrazines, and other water pollutants having an average pore radius between 15 and 30 .ANG..
U.S. Pat. No. 5,464,605 (Hayden) entitled PROCESS FOR THE DECOMPOSITION AND REMOVAL OF PEROXIDES discloses a process for decomposition and removal of peroxides from a gaseous or liquid media by contacting the media with a carbonaceous char which is made by carbonizing a bituminous coal at temperatures below 700.degree. C. in the presence of an oxidant gas, oxidizing the coal at temperatures below 700.degree. C. during or after the carbonization, and contacting the carbonized coal with a nitrogen compound and raising the temperature above 700.degree. C. The resulting material is then activated to the desired density at temperatures above 700.degree. C. in steam and/or carbon dioxide.
U.S. Pat. No. 5,064,805 (Otowa) entitled PRODUCTION OF HIGH QUALITY CARBON discloses a high quality activated carbon produced by starting with coconut shell char and activating with potassium hydroxide.
U.S. Pat. No. 4,978,649 (Surovikin) entitled POROUS CARBONACEOUS MATERIAL discloses an activated carbon produced by a process that increases the proportion of pores with a size greater than 200 .ANG..
U.S. Pat. No. 5,837,741 (Schwarz) entitled COMPOSITE MICROPOROUS CARBONS FOR FUEL GAS STORAGE discloses a method of making a microporous carbon material from a precursor which is either a crystalline salt of an aromatic sulfonate or a nonporous polymeric salt.